The use of water resistant corrugated paperboard for packaging has increased tremendously in the last several years. Accompanying this increased usage has been the demand for stronger and more specialized products to withstand more rigorous conditions. This demand has been met by the corrugated board industry by furnishing multiwall and heavy weight corrugated paperboard.
However, when such products are manufactured by the corrugators, the production rate is much lower than when single faced or double faced paperboard is being produced. Thus, the equipment is operating much less efficiently when such products are being made. The vast majority of water resistant corrugating operations are carried out using starch-based adhesives containing ureaformaldehyde, resorcinol-formaldehyde, or ketone-formaldehyde or other water proofing reagents to glue the various plies of paper or paperboard together. Such a standard water resistant corrugating adhesive is usually made by first cooking a portion of the starch with alkali to form a gelatinized phase called the carrier, which is then blended with uncooked starch (the raw portion). Most standard water resistant corrugating adhesives utilize unmodified starches for the carrier and raw portions. However, the use of slightly acid modified starches having a fluidity in the 4 - 10 range has been practiced as set forth in the patent of Merle J. Mentzer assigned to Corn Products Co., bearing U.S. Pat. No. 3,155,527. The water proofing agent can be added to the final mix or can be added in parts to the mix as it is being prepared and reacted in situ.
The carrier serves as a suspending agent for the uncooked starch. These adhesives require heat to gelatinize the raw starch to activate it as a bonding agent and to remove the water from the adhesive film in order for the plies to adhere to each other. When making multiwall board or board having especially heavy liners, the heat transfer rate to the adhesive is reduced substantially by the insulating effect of the paper.
It is the principal object of this invention to provide a water resistant adhesive composition which allows the production of multiwall and heavy weight corrugated paperboard at greater rates than presently attainable.